Cellular wireless communication devices, such as a mobile phones and personal digital assistants have become increasingly common in recent years. In general, a cellular wireless device communicates over an air interface with a base station, which provides the device with access to network resources, such as a communication channel to interact with other devices or with network servers.
In a typical cellular wireless communication system, multiple base stations are positioned throughout a market area, and each base station radiates to define a cell, including one or more cell sectors, in which cellular wireless devices can operate. One or more base stations are then typically coupled or integrated with a base station controller, which manages air interface operation such as use of air interface channels and handoff of devices between sectors. In turn, one or more base station controllers may be coupled with a switch (e.g., mobile switching center) or gateway (e.g., packet data serving node) that provides connectivity with a transport network such as the public switched telephone network (PSTN) or the Internet. With this arrangement, a cellular wireless device may communicate via a base station, base station controller, and the switch or gateway, with entities on the transport network.
Air interface communication between the base station and a cellular wireless device may operate in accordance with various air interface protocols, well known examples of which include CDMA (e.g., 1xRTT, 1xEV-DO), iDEN, WiMAX (e.g., IEEE 802.16), TDMA, AMPS, GSM, GPRS, UMTS, and EDGE, among others.
Typically, air-interface communications in each sector are encoded in a manner that distinguishes the communications in that sector from those in adjacent sectors. Further, air-interface communications to and from the base station may be divided into various control and traffic channels, typically through additional encoding or multiplexing. For example, in each sector, a base station may regularly emit a pilot signal that identifies the sector, and devices within range of the base station may then regularly monitor the pilot signal strength as a basis to determine whether to operate in that sector. As another example, to support data or voice communications between a served device and other devices or network servers, the base station may assign the device to communicate on a particular air-interface traffic channel. Further, devices in a sector may send control signals, such as pilot strength measurement messages and traffic channel assignment requests, to the base station via an air-interface access channel, and the base station may send control signals, such as page messages and traffic channel assignment messages, to the devices via an air-interface paging channel.
An important feature of contemporary cellular wireless networks is an ability to locate the geographical position of a mobile station. Such a feature was initially developed to assist emergency services in locating a mobile station. However, the availability of location information to support E911 services has given rise to the development of many other location-based services as well.
For instance, given the location of a mobile station, a location-based service provider/application (e.g., a cellular wireless carrier or third party) in communication with mobile station can provide the mobile station user with a report of weather or traffic in the user's vicinity. As another example, a location-based service provider can report a list of services or establishments (e.g., restaurants, parks, theatres, etc.) in the user's vicinity. And as still another example, a location-based service provider can provide a mobile station user with a map of the user's location or with directions for travel between the user's location and another location.
Typically, a wireless carrier will operate a positioning system that is arranged to determine and report mobile station locations to location based service provider (LBSP) applications (such as 911 service centers or commercial location based information providers). The positioning system may include a mobile positioning center (MPC) and a position determining entity (PDE), which may be integrated together, or may take other forms. And the positioning system may function to determine the location of a given mobile station based on various factors and with varying degrees of granularity.
In usual practice, when a mobile station seeks a location based service (such as an emergency aid dispatched to the mobile station's location, or download of content established or selected based on the mobile station's location), the mobile station may send a location-based service request via a wireless packet data connection to the LBSP (or to another entity, which may send the request (e.g., a derivative of the request) to the LBSP). In response to receipt of that request, the LBSP may then send a query to the mobile station's positioning system, seeking the location of the mobile station. In turn, the positioning system may then invoke a process to determine the mobile station's location and, upon determination of the mobile station's location, may report the location in a response to the LBSP. Based on the mobile station's location, the LBSP may then provide a location-based service (such as delivering emergency aid to the mobile station's location, or delivering to the mobile station content established or selected based on the mobile station's location).
A typical positioning system will determine the location of a mobile station through a triangulation process that takes into account base station signal delay measurements taken and reported by the mobile station. In particular, using known techniques (based on evaluation of signal phase or the like), the mobile station will measure the time that it takes for signals to travel respectively over the air from each of multiple cellular base stations to the mobile station, and the mobile station will report those base station delay measurements to the positioning system. Using those delays, along with the known speed of the signals, the positioning system may then compute the distance between the mobile station and each base station. In turn, for each base station, the positioning system may programmatically define an arc centered around a known fixed position of the base station and having a radius extending the distance from that position to the mobile station. The positioning system may then estimate the mobile station's location as the intersection of those arcs.
In many cases, mobile station location estimated in this manner is sufficient to facilitate providing a location based service. For instance, the estimated location may be sufficient to enable a computer to perform a database lookup to find pizza restaurants or other attractions or points of interest in the mobile station's vicinity, and to deliver that information to the mobile station. Likewise, the estimated location may be sufficient to facilitate dispatch of emergency personnel approximately to the location of the mobile station.
In other cases, it may be desirable to determine the mobile station's location with greater granularity (i.e., with greater precision). To do so, the positioning system may use the estimated location to determine which GPS satellites (or other such satellites) should be in the sky over the mobile station, and the positioning system may then direct the mobile station to tune to those satellites so as to receive satellite signal data. Once the mobile station receives the necessary satellite signal data, the mobile station may then report the data to the positioning system, and the positioning system may then use the satellite signal data as a basis to more accurately compute the mobile station's location.
In any event, the process of determining a mobile station's location may still involve at a minimum considering cellular base station signal delay measurements. Consequently, once the positioning system receives a request for a mobile station's location, the positioning system must generally send a request to the mobile station seeking those delay measurements and would then receive the delay measurements in response from the mobile station. Several mechanisms are well defined to facilitate that request/response communication between the positioning system and the mobile station.
According to one mechanism, known as “control plane” signaling, the positioning system will query a home location register (HLR) to determine the switch that is currently serving the mobile station. The positioning system will then engage in control signaling communication with the switch, possibly according to the well known industry standard 3GPP2 X.P0002/TIA PN-4747 (IS-881) or another standard, to provide a request message (e.g., an IS-881 “SMDPP” message) seeking the desired base station delay measurements from the mobile station. Upon receipt of the request from the positioning system, the switch may then engage in control signaling over the air interface with the mobile station, possibly according to the well known IS-801 standard, to send a position determination (PD) request message seeking the requested base station delay information from the mobile station. The mobile station may then respond by transmitting the base station delay information in an IS-801 PD response message to the switch, and the switch may then send that base station delay information in an smdpp response message to the positioning system.
According to another mechanism, known as “user plane” signaling, the positioning system and mobile station may engage in a higher layer direct communication with each other, through use of Short Messaging Service (SMS) signaling (e.g., via an SMS controller) and/or through IP communication (via a packet-switched network), so that the positioning system can request the data more directly and the mobile station can send the requested data more directly to the positioning system. For instance, the positioning system may send to the mobile station a specially coded SMS message that will trigger the mobile station to respond directly to the positioning system with a mobile originated SMS message that provides the positioning system with certain data, such as base station delay measurements.
While these mechanisms should work well to supply the positioning system with base station delay measurements so as to facilitate determination of mobile station location, the communication between the positioning system and the mobile station itself contributes to the overall latency in responding to a request for mobile station location and thus to the overall latency in responding to a location based service request.